Phenomenological kinetics of complex systems: the development of a generalized severity parameter and its application to lignocellulosics fractionation

Abstract The modelling of complex reaction systems, either homogeneous or heterogeneous, is possible only when the sequence of all of the elementary steps is established. Few complex reactions have, however, a known and unambiguously determined set of elementary steps. Modelling of such complex systems is essentially phenomenological; thus, the estimated kinetic parameters lack mechanistic meaning and are functions of the ranges of experimental conditions used. Confronted with this situation, industrial applications of such complex reactions have adopted the use of severity factors which try to combine into a single parameter the effect of the different operational variables. In what follows we shall focus on the application of the reaction ordinate to the case of biomass fractionation leading to hemicellulose solubilization. We shall propose a new, generalized severity parameter which accounts for the acid catalyst effect on the extent of reaction. Despite the fact that the kinetics of complex systems are essentially phenomenological, we present here an approach derived from basic kinetic principles.